The broad goal of the project is to understand the mechanisms by which RNA binding protein RBM3 regulates gene expression at the posttranscriptional level of mRNA stability and translation in cancer cells. We have identified that overexpression of the protein causes a normal cell to undergo a transformed phenotype resulting in the cells forming tumors in immunocompromized mice. On the other hand, knockdown of RBM3 expression results in cell death due to mitotic catastrophe. RBM3 interacts with HuR and hnRNP A1, and with AU-RNA sequences to enhance mRNA stability and translation of AU-rich transcripts such as COX-2, VEGF and IL-8. In addition, RBM3 overexpression increases the activation of the mammalian target of rapamycin protein in a Notch dependent mechanism. We have also identified microRNAs regulated upon RBM3 overexpression, including downregulating one that inhibits its own expression. Our studies also suggest that RBM3 is regulated at the posttranslational levels of phosphorylation, ubiquitination and SUMOylation. Based on these observations, we propose three specific aims. In Aim 1, we will determine the mechanism by which RNA binding protein RBM3 regulates gene expression. Here, we will identify the RNA sequences that interact with RBM3. In addition, we will determine the sequenced in COX-2 3'UTR that are required for RBM3-mediated COX-2 mRNA stability and translation. We will also identify the role of HuR and hnRNP-A1 in the process. In Aim 2, we will determine the residues in RBM3 that undergo phosphorylation, ubiquitination and SUMOylation by mutagenesis. We will also determine the effect of the mutants on mRNA stability and translation. In Aim 3, we propose to determine the mechanisms by which RBM3 induces tumorigenesis. We will use an xenograft cancer model to determine the role of mTOR and Notch pathway in RBM3 mediated tumorigenesis. Also, the role of microRNAs in the tumorigenesis will be determined. Completion of these experiments should give us a better understanding of how the RNA binding protein RBM3 functions in normal epithelial cells, and whether changes in the RBM3 expression that is observed in tumor cells is responsible for tumor behavior.